One possibility appears to be that you actually /don't/ have any CD key entered for your game. Meaning if we looked in the Windows registry on your machine, there is actually a blank/empty string for the CD key. This may have been the intentional or unintentional side-effect of using a CD key switcher or CD key generator at some point in the past.
(The currently installed CD key can be seen at [HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Electronic Arts\EA GAMES\Battlefield 1942\ergc] for the CD version of the game, or at [HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Electronic Arts\Origin\Battlefield 1942\ergc] for the Origin version of the game. Ignore and skip presence of the "Wow6432Node" subkey in that path if you're actually on a 32-bit version of Windows.)
The fact your CD key is blank/empty makes your CD hash (the MD5 hash seen by the BF1942 servers, and which you
generate using BFHasher when requesting an unban) equal to "d41d8cd98f00b204e9800998ecf8427e". If
you Google that MD5 hash value, you'll see that it's the correct MD5 hash of a blank/empty string.
Someone playing with a blank/empty CD key string was banned on the server recently, so the MD5 hash "d41d8cd98f00b204e9800998ecf8427e" is now banned. But that means any other "normal players" (I use that term loosely for many of the asylum inmates here) who were also using a blank/empty CD key have now become banned until they enter their correct CD key into their game installation.
The only real long-term answer is "don't play with an empty/blank CD key", because you'll always be subject to the bans of some other player who tries to use a blank string in order to play maliciously and/or circumvent their own ban. So even if the "d41d8cd98f00b204e9800998ecf8427e" key hash wasn't currently banned, it would become banned in the future, and/or will become banned again in the future.
Re-installing the game, taking care to enter in your CD key during installation, is the most "guaranteed" way to get the CD key recorded correctly. If you're using the Origin version, selecting "repair" installation from within Origin can get the Origin-assigned key correctly re-entered into the registry. If you prefer to use some other method, that may be successful too.
-Trench